1. Field of the Invention
The invention is related to a method for fabricating semiconductor substrate for optoelectronic components.
2. Description of the Related Art
In some radiation-emitting optical components, in particular in high-efficiency LEDs there is the problem that the light generated in the radiation-emitting structures is radiated in all spatial directions and thus also in the direction of the substrate, for which reason a large part of the light is lost in the case where absorbent substrates are used. This problem can be avoided by using transparent substrates. However, the disadvantages of some transparent substrates are that they have only a low electrical conductivity and/or an epitaxial deposition of the radiation-emitting structures is not possible owing to a lack of lattice matching. The problem of the lack of lattice matching for the deposition of epitaxial layers also occurs if absorbent semiconductor substrates are mirror-coated by the application of thin layers, for example of metal layers, at their top side in order to prevent the emitted radiation from penetrating into the substrate.
One possibility for avoiding this problem is disclosed in U.S. Pat. No. 5,376,580. In the method described therein, a radiation-emitting LED structure is firstly grown epitaxially on a lattice-matched growth substrate, then separated from the absorbent substrate and connected by means of wafer bonding to a substrate which has good electrical conductivity and is optically transparent to the relevant radiation. In this known method, however, the epitaxially grown LED structure, the electrical and optical properties of which, as is known, depends to a considerable extent on the crystal quality of the epitaxial layers, is subjected, during the separation of the absorbent substrate, to additional mechanical (for example grinding, polishing, etc.) and/or chemical method steps (for example etching), which may lead to damage to said structure.
A method for fabricating an optically transparent substrate onto which a semiconductor substrate can be grown epitaxially, and in which mechanical and/or chemical loading on the epitaxially grown semiconductor structure is avoided to the greatest possible extent, is specified in DE 100 08 583 A1. In the method described therein, firstly a substrate layer is grown on a lattice-matched substrate. The substrate layer is connected to the transparent substrate by means of wafer bonding on the side remote from the lattice-matched substrate. Afterward, the lattice-matched substrate is removed from the connection formed by substrate layer and transparent substrate and the radiation-emitting semiconductor structure is grown epitaxially onto the uncovered side of the substrate layer.
However, the known methods, in which the original provisional substrate is stripped away, require a comparatively high technical outlay. Moreover, transparent substrates are in some instances significantly more expensive than absorbent semiconductor substrates, so that the use of absorbent substrates may often be economically advantageous.